Biocompatible Coating of Medical Devices

ABSTRACT

A coated implantable medical device is described, wherein the coating comprises a coating matrix and particles of one or more molecular sieves, preferably zeolite of zeogrid particles, optionally loaded with one or more bioactive agents. The coating matrix itself can function as a second drug-carrying interface. The coating comprising the molecular sieve material has an excellent biocompatibility and allows suitable drug delivery into the body of an animal, preferably a mammal and most preferably a human.

FIELD OF THE INVENTION

This invention relates to the coatings for the human and veterinarymedical devices, which are to be introduced into or implanted in a humanor animal body, and especially such devices as will come into contactwith circulating blood supply and more particularly to those deviceswhich provide drug release, e.g. devices incorporating biologicallyactive, therapeutic or similar agents in said coatings. Further thepresent invention relates to methods of making the materials of suchcoatings and of applying such coatings to medical devices.

BACKGROUND

It has become a trend to treat a variety of medical conditions byintroducing an implantable medical device partly or completely into thebody cavity such as oesophagus, trachea, colon, biliary tract, urinarytract, vascular system or other location within a human or veterinarypatient.

For example, many treatments of the vascular system entail theintroduction of a device such as a stent, catheter, balloon, guide wire,cannula or the like. For instance classical treatments forartherosclerosis include medical therapies with balloon-dilatationsoptionally involving stent-implantation and coronary bypass surgery.Artherosclerosis is one of the most important causes of death in theWestern world. Coronary artherosclerosis is the result of a progressivedegeneration of the vessel wall which causes the occlusion of thearteries with different substances including lipids, cholesterol,calcium and different types of cells including smooth muscle cells andplatelets. Classical treatments include medical therapies,balloon-dilatations optionally involving stent-implantation and coronarybypass surgery.

Balloon-dilatations or percutaneous transluminal angioplasty (PTA) isbeing applied more and more and consists of breaking up and/or removingalready formed deposits along arterial walls using a balloon attached toa catheter that is introduced to a patient percutaneously and threadedthrough the arteries to the occluded site, where the balloon isinflated. An important limitation of this technique however is the highrisk of re-closing (restenosis) of the treated artery. Thus,balloon-angioplasty does not always lead to a permanently opened artery.Though systemic drug therapy has been developed to reduce thisrestenosis reaction it has not shown convincing results, mostly becauseof unwanted side effects in other parts of the body while theconcentrations in the blood vessel wall at the site of occlusion weretoo low to be effective.

In order to prevent the re-closing of the arteries, scaffolding devicescalled stents have been developed which are introduced into the lumen ofthe artery to keep them open. Unlike the balloon-catheter, the stentremains in the body as a permanent prosthesis.

Stents coatings have been developed for different purposes. Firstly, inorder to reduce allergic or immunological reactions to the stentmaterial, biocompatible polymers have been used to improve thebiocompatibility of the stent. A coating substance may also add to thestrength of the stent, or make its surface smoother, allowing easierintroduction into the vessels.

The use of stents to permanently maintain the opening in the lumen ofarterial walls has not completely eliminated the problem of restenosis.Apparently, introduction of the stent itself often causes damage to theinner lining of the vessel wall, inducing a ‘reparatory’ reactionleading to platelet aggregation and the migration of vascular smoothmuscle cells into the arterial lumen, where they accumulate and causeocclusion of the vessel. While the accumulated platelets can produceinflammatory mediators, the damaged endothelium recruits monocytes andleukocytes to the injury site, further contributing to neointimalhyperplasia.

The problem of stent-induced restenosis has been addressed in differentways. Irradiation therapy has been suggested based on intravascularlow-power red laser light (LPRLL), using a liquid sodium 186Reperrhenate solution as beta emitter, or potentially gamma radioactivestents made of platinum-iridium. Use of radioactive materials inintimate contact with body tissue over long periods is not preferred.

Alternatively, local drug delivery by the stents themselves has beensuggested. Bare metallic stents can be used as a platform to deliverdrugs locally where the stents struts enter the vascular wall providinga high drug concentration around the stent struts. Though bare stentscan be loaded with a drug without using a carrier interface, the amountof drug loaded this way is low and the release curve fast and notcontrollable (De Scheerder et al. 1996, Coron Artery Dis 7(2):161-166).Most drug eluting stents therefore use a drug carrying interface, e.g. acoating. Coated stents can be loaded with a larger amount of drug anddrug release can be better modified to obtain a more optimal drugrelease profile resulting in more prolonged effective tissue druglevels. Moreover, this form of drug-delivery is not limited torestenosis-inhibiting compounds.

A number of biocompatible materials suitable for the coating ofimplantable medical devices have been developed. More particularly, inthe field of stent-coating several materials have been tested for drugdelivery-characteristics either in animal models only or also inclinical trials, such as phosphorylcholine (PC), polylactide orpolylactide copolymers and fluorinated polymethacrylates PFM-P75.

More recently elastomeric poly(ester-amide) (coPEA) polymers andpoly-bis-trifluorethoxy phosphazene (PTFEP) have been shown to have therequired biocompatibility characteristics and have been suggested as acandidate for local drug delivery. Using stacked layers of polymer itwas been demonstrated that the pharmacokinetics of the drugs could bemanipulated.

Different drugs have been tested using local delivery from stentcoatings to reduce neointimal hyperplasia, including anti-proliferative,immunosuppressive, anti-thrombotic and anti-inflammatory drugs. Heparinhas shown only limited benefits in clinical trials.

Use of poly(organo)phosphazene coating impregnated with thecorticosteroid methylprednisolone was shown to result in a significantlyreduced neointimal thickening over the long term (6 weeks) afterstenting of pig coronary arteries (De Scheerder et al. 1996, CoronaryArtery Disease 7(2):161-166). More recently, local delivery of a highdose of methylprednisolone from phosphatidyl choline-coated stents orPMF 75 spray-coated stents was found to effectively decreaseinflammatory response and result in a significant reduction ofneointimal hyperplasia.

Other new drugs also appear to be promising. Recent studies haveevaluated these drugs as to their release kinetics, effective dosage,safety in clinical practice and benefit. These studies include trials onsirolimus or rapamycin (RAVEL, SIRIUS), Actinomycin D (ACTION),Tacrolimus (PRESENT), Placitaxel and derivatives (SCORE, ASPECT, ELUTE),dexamethason (EMPEROR), everolimus (FUTURE).

Estrogen inhibits intimal proliferation and accelerates endothelialregeneration after angioplasty. 17Beta-estradiol-elutingphosphorylcholine coated stents were found to be associated with reducedneointimal formation. Gene therapy on the vessel wall by local deliveryof DNA has also been considered. Effective transfection of neointimalcells was demonstrated using plasmid DNA loaded Polylactic-polyglycolicacid (PLGA) as stent coating.

WO 03/035134 describes a stent coating composition comprising abiodegradable carrier and a bioactive component. The biodegradablecarrier is either polymeric or non-polymeric and examples ofnon-polymeric carriers are vitamin E or derivatives thereof, peanut oil,cotton-seed oil, oleic acid- or combinations thereof.

One of the drawbacks of conventional means of drug delivery using coatedmedical devices however, is the difficulty in effectively delivering thebioactive agent over a short term (that is, the initial hours and daysafter insertion of the device) as well as over a long term (the weeksand months after insertion of the device). Another difficulty with theconventional use of stents for drug delivery purposes is providingprecise control over the delivery rate of the desired bioactive agents,drug agents or other bioactive material.

In view of the potential drawbacks to conventional drug deliverytechniques, there exists a need for a mechanism for controlling therelease rate of the drugs for implantable medical devices to increasethe efficacy of local drug delivery in treating patients. There is aneed for a device, method and method of manufacture which enable acontrolled localised delivery of active agents, drug agents or bioactivematerial to target locations within a body.

SUMMARY OF THE INVENTION

The present invention provides compositions for coating of implantablemedical devices, which present a number of advantages over the prior artcoatings. More particularly, the coating compositions of the presentinventions are biocompatible and are suited for loading and controlleddelivery of bioactive agents. Most particularly, the coatingcompositions of the present invention have been found to demonstrate ananti-restenotic effect per se, making them particularly suited for thecoating of endovascular medical devices.

A first aspect of the invention thus relates to coating compositions formedical devices, most particularly implantable medical devices, i.e.devices which are to be introduced partially or completely into thehuman body. The coating compositions of the present invention comprise acoating matrix and particles of one or more molecular sieves. Theparticles of the one or more molecular sieves are either embedded withinthe coating matrix or are covered by the coating matrix.

According to a second aspect of the present invention, the coatingcompositions comprising a matrix and particles of one or more molecularsieves are used as drug delivery (and optionally drug storage)compositions. Thus, the present invention provides compositions fordelivering therapeutic agents into the body of a mammal. Thecompositions of the invention are biocompatible and are preferablyapplied to an implantable medical device, such as a stent or a vascularor other graft sheath, among other configurations. The compositions maybe used as coating for human and veterinary medical devices, especiallydevices that are to be introduced into or implanted in a human or animalbody, especially such devices as will come into contact with circulatingblood supply. Thus the compositions of the invention are particularlybiocompatible with the endovascular environment.

According to a particular embodiment of the present invention, thecoating composition comprises a coating matrix which is a hydrophobicmatrix. Most particularly such a hydrophobic matrix is acis-hydrogenated Omega-3 fatty acid.

According to the present invention, the coating composition comprises acoating matrix and particles of one or more molecular sieves. Mostparticularly such a sieve is a (ultra and/or super-microporous material,preferably a zeolite or a zeogrid, as described in the examples of thisapplication.

According to a particular embodiment of the invention the particlesand/or the coating matrix can optionally further comprise, one or morebioactive agents. According to a most particular embodiment of thepresent invention, the molecular sieve and optionally the coating matrixare loaded with the same or a different drug to be released. Furtherspecific embodiments relate to the loading of hydrophilic drugs in themolecular sieve embedded in or covered by a hydrophobic matrix on thesurface of an implantable medical device.

According to one embodiment of the present invention, the particles ofthe one or more molecular sieves or the matrix comprising the particlesof the molecular sieves are present essentially only within structuralcavities in the surface of an implantable medical device.

According to another aspect of the present invention, methods areprovided for the controlled release of one or more bioactive agents froman implantable medical device. The controllable release is achieved byone or more of the following factors a) the combination of the molecularsieve with the matrix, b) the selection of the pores of the molecularsieve particles, or the selection of the size of the molecular sievematerials and c) the adjustment of the biosolubility kinetics of thematrix.

An object of present invention is thus to provide medical devices whichare coated with a biocompatible coating composition, i.e. which resultsin minimal reactivity of the environment in which the medical device isplaced. A further object of the invention is to provide a medical devicewhich is coated with a coating composition which can be loaded with andwhich can release a suitable bioactive agent. Thus, according to thepresent invention, the implants are coated with a coating compositioncontaining a means which acts as a drug reservoir and ensures drugrelease, preferably in a controlled manner. The present invention thusprovides devices and methods for reliably delivering suitable amounts ofone or more bioactive agents such as therapeutic agent or drug directlyinto a body portion during or following a medical procedure, so as totreat or prevent such conditions and diseases, for example, to preventabrupt closure and/or restenosis of a body portion such as a passage,lumen or blood vessel or to prevent bacterial infection.

According to one embodiment of the present invention, the implantabledevice is a pitted stent. The surface of the pitted stent is perforatedby holes or pits which is filled with the coating composition of thepresent invention to increase the load of therapeutic agent and/or tocontrol its release. According to a particular embodiment the pittedstent is a radially expandable prosthesis with reservoirs made in theouter surface for containing therapeutic agents described in WO0166036and EP1348405.

Yet a further aspect of the present invention relates to methods ofmaking the coatings of the present invention and methods of applying thecoatings of the present invention to implantable medical devices.

Yet another aspect of the present invention relates to methods forpreventing adverse reactions to an implanted device, which methodscomprise coating the device with a coating composition of the presentinvention comprising a coating matrix and particles of one or moremolecular sieves, optionally loaded with a bioactive agent. Moreparticular embodiments of the invention relate to methods for preventingrestenosis upon implantation of an endovascular prosthesis, which methodcomprises coating the prosthesis with the coating compositions of thepresent invention prior to implantation. The invention further relatesto the use of a coating matrix and particles of at least one molecularsieve, more particularly of a silicate molecular sieve material, mostparticularly of a zeogrid, in the coating of implantable medical devicesfor the sustained release of a bioactive agent.

DETAILED DESCRIPTION

The present invention relates to biocompatible coatings for implantabledevices comprising a coating matrix and particles of one or moremolecular sieves. According to a particular embodiment the coatingmatrix and/or particles are loaded with a bioactive agent.

The term “bioactive agent” is used herein to mean any agent such as apharmaceutical agent or drug or other material that has a therapeuticeffect. It thus includes, but is not limited to, chemical compounds,DNA, RNA, vectors comprising DNA or RNA, antibodies, etc. Alternativelythe bioactive agent may be an agent for use in detection, e.g. a label,such as a contrast agent, a luminescent or fluorescent agent etc.

“Biocompatible” as used herein relates to the fact that it iswell-tolerated in the body, i.e. that does not have a toxic or injuriouseffect on the biological system. However, depending on the application,requirements of compatibility may vary. Thus, in some situationsbiocompatibility may also imply the ability of a material to performwith an appropriate host response, i.e. which can interact with and intime be integrated into the biological environment. In this regardmedical devices used for implantation into the cardiovascular system canbe considered to have particular requirements. Thus, ‘endovascularbiocompatibility’ and more particularly ‘cardiovascular compatibility’,when used to describe a material herein relates to the fact that thematerial does not, or only to a very limited extent, induce reactionswhich are typically observed in the endovascular system in response tothe introduction of a foreign object and which are undesired for theappropriate functioning of the vessel and the medical device implantedtherein. These reactions include and can be measured as damage of thevascular wall, inflammation, reduction of the lumen area, neointimalhyperplasia, and area stenosis.

The term “implant” or “implantable medical device” as used herein refersto any device which is intended to be introduced and optionallyimplanted into the human body, including devices used for implantationinto vessels, ducts or body organs, such as a stent, catheter, canunula,vascular or arterial graft sheath, a device for implantation into theoesophagus, trachea, colon, biliary tract, urinary tract, orthopaedicdevices etc.

A “stent” as used herein refers to an implantable medical device used tosupport a structure within the human or animal body, such as but notlimited to the oesophagus, trachea, colon, biliary tract, urinary tract,vascular system or other location within a human or veterinary patient.A particular embodiment of the invention relates to a vascular stent,more particularly a stent for use in supporting coronary arteries.

A pitstent or pitted stent as used herein refers to a stent comprising(perforating) holes or non-perforating (pits) openings in its outerand/or inner surface.

The term “molecular sieve” as used herein refers to a solid with poresthe size of molecules. It includes but is not limited microporous andmesoporous materials, ALPOs and (synthetic) zeolites, pillared ornon-pillared clays, clathrasils, clathrates, carbon molecular sieves,mesoporous silica, silica-alumina (for example, of the M41S-type, withan ordered pore system), microporous titanosilicates such as ETS-10,urea and related host substances, porous metal oxides. Molecular sievescan have multimodal pore size distribution, also referred to as orderedultramicropores (typically less than 0.7 nm) supermicropores (typicallyin the range of about 0.7-2 nm) or mesopores (typically in the range ofabout 2 nm-50 nm). A particular type of molecular sieves envisagedwithin the present invention are the silica molecular sieves, moreparticularly silica zeogrids and/or zeolites.

A “zeogrid” is a silica superstructure with a combination of super- andultra-micropores and with an X-ray diffraction pattern typical of alayered structure, such as in FIG. 1 (see also Kremer et al. Adv. Funct.Mater. 2002, 12:286). Supermicropores have free diameters in the rangeof typically 7 to 20 Å, ultramicropores have free diameters of less than7 Å, identifiable by Nitrogen-adsorption (Rouquerol & Rouquerol,Adsorption by powders and porous solids, 1999, Sing, Academic Press).

A “zeolite” can be defined as a crystalline material of which thechemical composition includes essentially aluminium, silicon and oxygen.Typically, zeolites are described as aluminosilicates with a threedimensional framework and molecular sized pores. Nomenclature ofmolecular sieves Molecular sieves Pore size Microporous <20 Å Mesoporous20-500 Å Composition Al & Si Al & P Al & Si Al & P aluminosilicatealuminophosphate Name zeolites AlPOs Mesoporous

The term ‘matrix’ as used herein refers to a material suitable for thecoating of an implantable device, i.e. a material that is biocompatibleand can be applied to the surface of an implantable device so as toobtain a coating.

The present invention is based on the observation that molecular sievessuch as supermicroporous or ultramicroporous silicate material can beused in the coating of medical implants and is biocompatible. It hasbeen observed that medical devices coated with the coating compositionsof the present invention, when implanted in a porcine coronary vessel,did not result in a significant damage of the vascular wall, that noincreased inflammatory reaction was observed, that there was nosignificant reduction of the lumen area, and that neointimal hyperplasiaand area restenosis were not significantly increased compared to barestents. To the contrary, it was observed that the use of molecularsieves, more particularly the use of silicate zeogrids resulted in lessarea stenosis than the control groups without the molecular sieves,indicating an anti-restenotic effect of the molecular sieve-comprisingcoating material.

The present invention is further based on the observation that molecularsieves, i.e. particles of porous material, more particularly(super/ultra) microporous silicate material, such as zeolites orzeogrids, can be loaded with a bioactive agent such as a drug, forinstance, β-estradiol and can be used to ensure a controlled (i.e.sustained) release profile for the loaded bioactive agent (and thus actas a drug carrying interface).

A particular embodiment of the present invention thus relates to acoating composition of an implantable medical device comprisingmolecular sieve particles that comprise a bioactive agent or drug,wherein release of said drug is controlled. Controlled release as usedherein refers to a release that is adjusted to the requirements of thepurpose of the drug. For instance, controlled release can refer tosustained release, i.e. release that does not occur immediately, e.g.more than 25% within the first 24 hours. Controlled release of abioactive agent comprised in a zeogrid or zeolite embedded in a matrixcan be demonstrated in an in vitro setting as shown in the examplesbelow. Controlled release of one or more bioactive agents is obtained bymodulating one or more of the following a) the structure of themolecular sieve particles (pore, structure size), b) the properties ofthe matrix material (biostability/biodegradability, density, thickness)and c) the nature of the loaded bioactive agents relative to the natureof the matrix material (hydrophilicity).

As indicated below, a combined release pattern (e.g. both immediaterelease from the matrix and controlled release from the molecular sieveparticles embedded therein) is also envisaged within the context of thepresent invention.

Moreover, the use of molecular sieves significantly increases thedrug-loading capacity of the medical device. Application of the presentinvention to medical devices with structural cavities can furtherimprove the loading capacity of the medical device. For instance, apitted stent coated by a hydrophobic matrix (optionally loaded with adrug) and a zeolite or zeogrid loaded with a drug has an increased drugloading capacity as compared to classic (non-pitted stent) stents coatedby a hydrophobic matrix loaded with drug or even a pitted stent coatedby a hydrophobic matrix loaded with drug. Thus the present inventionprovides implantable devices which allow increased (i.e. over longerperiod of time or of higher amounts) of drug delivery.

According one aspect of the present invention, the molecular sieves arethus used as reservoirs and delivery systems for bioactive agents andcan be selected so as to ensure controlled release of the bioactiveagents. The size of the pores within the molecular sieve can be selectedso as to ensure a faster or slower release of the bioactive agent.Zeogrid and MCM-22 are particular suitable molecular sieves for the usein present invention. The preparation and characterisation of MCM-22samples has been described by S. Laforge, et al. Microporous andMesoporous Materials Volume 67, Issues 2-3, 6 Feb. 2004, Pages 235-244.U.S. Pat. No. 4,954,325 (1990) discloses that MCM-22 contains threeindependent types of pores: two-dimensional sinusoidal channels (4.1×5.1Å), large supercages (7.1 Å, 18.2 Å height) accessible through 10⁻MRopenings (4.0×5.5 Å) and large pockets on the external surface (7.1 Å, 7Å depth). Alternative molecular sieves envisaged within the context ofthe present invention include but are not limited to silicalite, ZSM-5zeolites, mordenite, zeolite L, zeolite X, zeolite Y, zeolite LSX,MCM-41 zeolites, silicoaluminophosphates (SAPOs), zeolite beta, zeoliteomega, ZSM-5, ZSM-12, MSM-36, MCM-49 . . . etc.

Molecular sieves can be synthesised with pore size suitable for aparticular release profile and optionally a particle size suitable forembedding into the matrix and/or incorporation in the cavities of theprosthesis.

Zeolites, such as MFI (silicalite-1, ZSM-5, TS-1), hydroxysodalite, LTA(zeolite A), MTW (ZSM-12), FAU, BEA (zeolite beta), LTL (zeolite L), andAFI (ALPO4-5), with particle size in the nano-scale range known from theprior art (JunPing Dong et al. Microporous and Mesoporous Materials,Volume 57, Issue 1, 2 January 2003, Pages 9-19).

The pore size of molecular sieves can further be influenced by thenature of the templating molecules in the synthesis of the mesoporous ormicroporous composition of this invention. The addition of swellingagents to the synthesis mixture can further affect the pore size of theresulting molecular sieve. Zeolites with different pore size have beenwell characterised and described by Martin David Foster in“Computational Studies of the Topologies and Properties of Zeolites”,The Royal Institution of Great Britain, Department of Chemistry,University College London, A thesis submitted for the degree of Doctorof Philosophy, London, January 2003. Suman K. Jana et al Microporous andMesoporous Materials Volume 68, Issues 1-3, 8 Mar. 2004, Pages 133-142describes how pore size can be controlled in molecular sieves,particular in Mesoporous MCM-41 and SBA-15 molecular sieves by the ofdifferent organic auxiliary chemicals such as methyl-substituted benzene(1,3,5-, 1,2,4- or 1,2,3-trimethylbenzene), isopropyl-substitutedbenzene (1-, 1,3-di- or 1,3,5-tri-isopropylbenzene) and alkane (octane,nonane, decane, tridecane, hexadecane or eicosane) as auxiliarychemicals.

Synthetic zeolites are currently produced as powders of micron sizecrystals and compacted into millimetre size extrudates or other forms ofpellets for applications as adsorbents and catalysts. In many of theseapplications, mass and heat transfer properties could potentially beimproved by forming the zeolite in a different way. Research in thisarea led already to significant achievements. Examples of alternativelystructured zeolite matter reported in recent literature are for exampledelaminated zeolites (A. Corma et al, Nature 1998, 396, 353.), supportedzeolite films and membranes (J. Caro et al, Microporous MesoporousMater. 2000, 38, 3.), mesoporous-microporous hybrid structures withmicroporosity in walls of ordered mesoporous materials (Z. Zhang et al,J. Am. Chem. Soc. 2001, 123, 5014.) and nanosized zeolites such as thosesynthesized in confined space (I. Schmidt et al, Inorg. Chem. 2000, 39,2279). The common property of these alternative zeolite materials isthat at least in one dimension, the zeolite body is nanosized.

According to a particular embodiment of the present invention, zeolitesare used wherein all or part of the ion-exchangeable ions have beenreplaced with ammonium ions or metal ions (as described in U.S. Pat. No.4,938,958).

According to a particular embodiment of the invention the molecularsieve particles contain more than one bioactive agent. Before mixing inthe coating, the molecular sieve (e.g. microporous or mesoporous)particles are loaded with different drugs to obtain multipledrug-release. Alternatively, different layers of coating withmicroporous or mesoporous particles that contain different drugs canalso be applied. The drug-release from mesoporous or microporousparticles, can also be combined with drug release from the coating thatcontains the mesoporous or microporous particles.

According to the present invention the molecular sieves can either beembedded in a polymeric or non-polymeric matrix, that is loaded onto tothe implantable device or can be glued to the surface of the implantablemedical device and covered by a matrix, which can optionally furtherinfluence the release of the loaded bioactive agent. Examples ofbiocompatible glues for use in the context of the present inventioninclude fructose, glucose, sucrose, saccharose, lactose, maltose,dextrins and celluloses. Also, oils, fats, fatty acids orcis-hydrogenated oils are envisaged as gluing products. Subsequently,the glued layer of molecular sieve particles can be covered by abiocompatible matrix.

The coating compositions of the present invention comprise particles ofone or more molecular sieves and a coating matrix.

The coating matrix can be a hydrophobic matrix and consist essentiallyof (i.e. consist in at least 80% of) an oil or a combination of oilssuch as, but not limited to, a marine animal derived oil, a terrestrialanimal derived oil, a plant-derived oil, a mineral oil and a siliconeoil, or a combination of one or more of these oils. The matrix can be anoil (or a combination of oils) selected from the group consisting ofolive oil, soybean oil, canola oil, rapeseed oil, cottonseed oil,coconut oil, palm oil, sesame oil, sunflower oil, safflower oil, ricebran oil, borage seed oil, syzigium aromaticum oil, hempseed oil,herring oil, cod-liver oil, salmon oil, corn oil, flaxseed oil, wheatgerm oil, rape seed oil, evening primrose oil, rosehip oil, tea treeoil, melaleuca oil and jojova oil.

The matrix can also be an oil selected from the group consisting ofomega-3 oil and omega-6 oil. According to a particular embodiment of theinvention, the matrix additionally comprises a solidifying agent.Additionally or alternatively, the matrix used according to the presentinvention may be a totally or partially chemically hardened oil or fat,in particular a hydrogenated oil or fat.

Particular embodiments of the chemically hardened oil or fat maycomprise unsaturated fatty acid chains but be substantially free oftrans-isomers of unsaturated fatty acids, i.e. a cis-hydrogenated fattyacids. Thus, according to a particular embodiment the coating matrix ofthe present invention comprises at least 20% of one or morecis-hydrogenated fatty acids. The term ‘cis-hydrogenated fatty acid’(CHFA) as used herein relates to fatty acid compounds which areessentially free of trans-unsaturated double bonds. Fatty acid compoundscomprise esters, mono-, di- and triglycerides, phospholipids,glycolipids, diol esters of fatty acids waxes and sterol esters, moreparticularly oleic acid, stearic acid or any mixture thereof. Mostsuitable fatty acids are triglycerides having a length of 4 to 24 C. Thecis-hydrogenated fatty acids which are used for the coating of medicaldevices in the context of the present invention are, according to oneembodiment selected from mono-, di- or triglycerides or esters thereof.Most particularly, they are made up of between 20% and 95%triglycerides. The fatty acid can originate from vegetable oils, suchas, particularly soybean, sesame seed and peanut oil, but also includingsunflower seed, cottonseed, corn, safflower, palm, rapeseed or animaloils, such as fish oils and mixtures of such oils. Oils of mineralorigin or synthetic fats can also be employed as long as they aresufficiently biocompatible and/or non-toxic. According to a particularembodiment of the invention, the cis-hydrogenated fat can comprises oneor more cis-hydrogenated omega-3 fatty acids, particularly, but notlimited to cis-hydrogenated forms of eicosapentaenoic acid (EPA) anddocosahexaenoic acid (DHA). According to a more particular embodiment ofthe invention, the fatty acid comprises a substantial amount of omega-3fatty acids. Oils obtained from cold water fish are generally rich inomega-3 fatty acids. Cod liver oil comprises about 20% by weight ofomega-3 fatty acids.

Fatty acids with reduced level of trans-unsaturated double bonds can beobtained by influencing the hydrogenation conditions of oils to reducethe amount of trans-isomers formed (Puri P. J Am Oil Chem Soc55(12):865-), by use of metal alloy catalysts or adding modifiers orammonium compounds (U.S. Pat. No. 4,307,026). In WO 98/54275, however, aprocess is described which enables the significant reduction orelimination of trans-unsaturated fatty acid compounds from a substratecontaining cis and trans isomers by means of a zeolite material.

Additionally or alternatively, the matrix may be enriched with naturalor biologically safe fatty acids and particularly be enriched with DHA(22: 6n-3 docosahexenaenoic acid) and/or EPA (20: 5n-3; Eicosapentaenoicacid) which are known to have significant antithrombotic andanti-atheriosclerotic effects and have been known to significantly blockmitogenic effects of serotonin. Alternatively the matrix is a silicon, asilicon elastomer or a silicon blend. These silicones may comprise oneor more adjuvant polymers. Polymers are biocompatible (i.e., not elicitany negative tissue reaction or promote mural thrombus formation) anddegradable, such as lactone-based polyesters or copolyesters, e.g.,polylactide, polycaprolacton-glycolide, polyorthoesters, polyanhydrides;poly-aminoacids; polysaccharides; polyphosphazenes; poly(ether-ester)copolymers, e.g., PEO-PLLA, or blends thereof. Nonabsorbablebiocompatible polymers are also suitable candidates. Polymers such aspolydimethyl-siloxane; poly(ethylene-vinylacetate); acrylate basedpolymers or copolymers, e.g., poly(hydroxyethyl methylmethacrylate,polyvinyl pyrrolidinone; fluorinated polymers such aspolytetrafluoroethylene; cellulose esters. Examples of suitablebiocompatible polymers or polymer combinations include but are notlimited to poly(vinyl pyrrolidone)/cellulose esters, poly(vinylpyrrolidone)/polyurethane, poly(methylidene maloleate),polylactide/polyglycolide copolymers, poly(ethylene glycol) copolymers,poly(ethylene vinyl alcohol) and poly(dimethylsiloxane)-based systems.

The matrix can be covered on the surface of the implantable medicaldevice or can be introduced into holes or reservoirs made (for instancedrilled) in the implantable medical device. According to the inventionthe matrix comprises or envelopes molecular sieves.

According to one embodiment of the present invention, the hydrophobicmatrix comprising the particles of porous material, is itselfadditionally loaded with a bioactive agent or drug, either the same drugor a different drug from that/those comprised in the porous material.This coating thus functions as a second drug-carrying interface.According to one particular embodiment of the present invention, theparticles of the molecular sieve hold a hydrophilic drug, while thecoating matrix holds a hydrophobic drug. According to a particularembodiment the particles of the molecular sieve comprise one or morenon-lipophilic drugs that are not particularly suited for localdrug-delivery from the coating, e.g. in the case of a cis-hydrogenatedomega-3-fatty acid-based coating. The combination of both releasesystems is particularly suitable to obtain a dual release of the same ora different drug and can be used to optimise drug release, e.g. forcounteracting unfavourable body reactions on the implant.

According to a further embodiment, the matrix can be covered by a secondlayer comprising a biocompatible polymer or a hydrophobic solution,which can be selected from the polymers described above. Such anadditional layer can be used as a third drug carrying interface.

According to one embodiment of the present invention, the matrixcomprising the molecular sieves is applied to an implantable medicaldevice comprising structural cavities in its (inner and/or outer)surface. According to this embodiment the matrix comprising themolecular sieves can be present both on the surface and in thestructural cavities therein. Alternatively, the matrix is presentessentially only in the structural cavities in the surface of theimplantable medical device. This can be achieved, removing the excesscoating material on the surface of the prosthesis in between the holesor pits of said device, after the latter have been filled, e.g. bywiping off or cleaning the coating material and thus obtaining anessentially non-surface-coated stent. Optionally, this stent is thenfurther coated with another second coating matrix (which is selectedfrom the coating matrices described herein). Alternatively, selectivefilling of only the structural cavities with the matrix can be achievedby selectively filling the pores using micro-injection techniques.

According to a particular aspect, the present invention relates to theuse of a coating for local drug-delivery for further optimisation of thedrug release from the medical device and for controlling the release inaccordance with the unfavourable body reaction.

A wide variety of drugs is envisaged for which local delivery from thecoating of an implanted medical device would be beneficial. Moreparticularly, in the context of implants, local delivery ofanti-inflammatory and immunomodulatory drugs has generally beendemonstrated to be beneficial. A wide range of drugs can be impregnatedand released by the coating of the present invention. In the applicationof the invention to drug-eluting stents (also referred to as DES), thetherapeutic agents envisaged suitable include but are not limited tocorticosteroids such as dexamethasone and methylprednisolone, drugs usedto prevent transplant rejection, such as cyclosporin, sirolimus,tacrolimus and everolimus, antiproliferative drugs such as vincristine,doxyrubicine, paclitaxel and actinomycin and metalloprotease inhibitors,such as batimastat. Other suitable therapeutic agents include sodiumheparin, low molecular weight heparin, hirudin, argatroban, forskolin,vapiprost, prostacyclin and prostacyclin analogues, dextran,D-phe-pro-arg-chloromethylketone, dipyridamole, glycoprotein Ib/IIb/IIIaplatelet membrane receptor antibody, recombinant hirudin, thrombininhibitor, angiopeptin, angiotensin converting enzyme inhibitors,calcium channel blockers, colchicine, fibroblast growth factorantagonists, histamine antagonists, HMG-CoA reductase inhibitor,methotrexate, monoclonal antibodies, nitroprusside, phosphodiesteraseinhibitors, prostaglandin inhibitor, serotonin blockers, steroids,thioprotease inhibitors, triazolopyrimidine, PDGF antagonists,alpha-interferon, genetically engineered epithelial cells, andcombinations thereof. Alternatively, the therapeutic agent for use inthe context of the present invention can be a nucleic acid, encoding oneor more therapeutic agents such as those described above or encoding amolecule which, when present in the cells of the tissues surrounding theimplantable device, has a therapeutic effect. According to yet anotherembodiment of the present invention the therapeutic agent can be acomposition comprising cells, such as (genetically modified) epithelialcells.

According to the present invention the bioactive agents used for loadinginto the molecular sieves can be either hydrophilic or hydrophobic.

Bioactive agents for loading into the hydrophobic matrix according toone embodiment of the present invention are preferably hydrophobic.Hydrophilic drugs may be coupled to the natural fatty acids to renderthem hydrophobic (lipophilic). DHA is a 22 carbon naturally occurringwhich is particularly suitable to this end as this unbranched fatty acidcan be used to attached drugs. DHA can for instance be attached via theacid group to hydrophilic drugs rendering these drugs more hydrophobic(lipophilic). For instance covalent conjugation of a natural fatty acidto paclitaxel is well known in the art (Bradley et al., Clin Cancer Res.2001 October; 7(10):3229-38) and procedure to link fatty acids to aminoacids, peptides, drugs and other compounds have been described inEP0712389.

According to a particular embodiment of the present invention, thebioactive agent comprised within the pores of the molecular sieve is notan inorganic anti-microbial agent, more particularly not a metal ion, ora metal salt.

Methods for obtaining a hydrophobic carrier or matrix are known to theskilled person. Such a method for obtaining an hydrophobic carrier canbe mixing a hydrophobic solvent with a solidifying agent at atemperature above its melting temperature so as to obtain a mixture andcooling the mixture. Such mixture may for instance contain 50-10 percentof said the hydrophobic solvent such as marine animal derived oil,terrestrial animal derived oil, plant-derived oil, mineral oil orsilicone oil and 10-50 percent of a solidifying agent by weight.

A particular method for obtaining an hydrophobic carrier can be mixing ahydrophobic solvent with a solidifying agent whereby both thehydrophobic solvent and the solidifying agent are brought to atemperature above the melting temperature of the solidifying agent.

Such solidifying agent can be selected from the group consisting of atleast one long chain fatty alcohol having at least 15 carbon atoms inits carbon backbone and at least one fatty acid, having at least 18carbon atoms in its carbon backbone.

The solidifying agent can be agents selected from the group consistingof at least one long chain fatty alcohol having at least 15 carbon atomsin its carbon backbone, at least one fatty acid having at least 18carbon atoms in its carbon backbone, an agent which has at least onealkyl group side chain in its carbon backbone, of an agent which has atleast one alkyl group side chain in its carbon backbone wherein saidcarbon backbone of said fatty acid or said fatty alcohol has at leastone hydroxyl group at position α and β, an agent which has at least onealkyl group side chain in its carbon backbone wherein said carbonbackbone of said fatty alcohol has at least one hydroxyl group atposition α and β, an agent which has at least one alkyl group side chainin its carbon backbone, wherein said carbon backbone of said fatty acidor said fatty alcohol has at least one hydroxyl group at positions 8-14and an agent including a 12-hydroxy fatty acid.

The hydrophobic solvent used to make the hydrophobic matrix can be anoil selected from the group consisting of olive oil, soybean oil, canolaoil, rapeseed oil, cottonseed oil, coconut oil, palm oil, sesame oil,sunflower oil, safflower oil, rice bran oil, borage seed oil, syzigiumaromaticum oil, hempseed oil, herring oil, cod-liver oil, salmon oil,corn oil, flaxseed oil, wheat germ oil, rape seed oil, evening primroseoil, rosehip oil, tea tree oil, melaleuca oil and jojova oil, preferablyit includes an oil selected from the group consisting of omega-3 oil andomega-6 oil

The present invention relates to the coating of implantable medicaldevices. A particular embodiment of the invention relates to animplantable medical device which is a vascular stent, more particularlya stent for use in supporting coronary arteries. Most commonly thestents are made out of metal or metal alloy, such as titanium, tantalum,stainless steel, or nitinol. According to a particular embodiment of thepresent invention the implantable device comprises one or a plurality ofstructural cavities, i.e. (perforated) holes or (unperforated) pits,which can be of different shapes including but not limited to a shapewherein the width is essentially the same as its length, (e.g. such asessentially round, square, polygonal) or a longitudinal shape whereinthe length is more than twice the size of the width, (e.g. grooves orslits). In the case of hollow implantable medical devices, such asstents, the cavities can be located on the inner and/or outer surface ofthe device. Examples include but are not limited to the designs such asdescribed in WO 98/36784, WO 01/93781, and WO02/32347. A particularembodiment of the present invention is a stent comprising struts withtiny laser-drilled holes throughout the stent, such as described inWO0166036 and EP1348405. More particularly, the implantable medicaldevice can be a radially expandable prosthesis.

Different stents designs have been described in the art which aresuitable for coating, optionally with drug-delivering compositions.Particularly suited in the context of the present invention are thestent designs described in U.S. Pat. No. 6,562,065, which relates topitted stents or stents comprising laser drilled holes for drug wells,and U.S. Pat. No. 5,728,150 which relates to a microporous prosthesis.The coating compositions of the present invention can be applied to thewhole stent and/or be used to fill the pits of the stent, optionallycarrying particular therapeutic agents as described below. Otherexamples of suitable stents include but are not limited to thosedescribed in WO02/060351, WO03/082152, WO 03/079936, WO 03077802, WO03072287, WO 03/063736, WO 03061528, WO 03/059207, WO 03/057078. Thesemoreover include stents which are available commercially and/or havebeen tested in clinical trials including but not limited to the NIRx®stent (Bostn Scientific, Natick, Mass.), Cordis Bx Velocity®, CookV-Flex plus®, S-Flex® and ChromoFlex® stent, Gianturco-Z®,Gianturco-Roche Z®, and Gianturco-RoubinII® stent.

According to a particular embodiment of the present invention, thecoating matrix comprises cis-hydrogenated fatty acids. As thesecis-hydrogenated fatty acids do not contain trans-unsaturated fattyacids, which have been demonstrated to be a potential health hazard,these fatty acids are particularly biocompatible. Coatings essentiallycomprising fatty acids moreover have the advantage that they are lesslikely to crack during expansion of the stent during fabrication,implantation and use. This also implies that no harmful fragments willbe released from the coating in the body. Fatty acid coatings can resultin a smooth layer, minimising the chances of damage to the surroundingtissues in the body, e.g. the endothelium in the case of a vascularstent.

The physicochemical properties of fatty acids strongly depend on thechemical structure of the fatty acid residues and more particularly ontheir chain length and the amount of double bonds present. According tothe present invention, the coating of the medical device has a wax-like(non-fluid) consistency, which is maintained within the body. Thus, themelting point of the fatty acid coating should be above bodytemperature, i.e. above 38° C., particularly between 38° C. and 52° C.,more particularly above 40° C. and below 50° C., e.g. between 40.6° C.and 47.6° C. By selecting the melting temperature of the coatingcomposition to be above body temperature, it is ensured that theproperties of the coating material are maintained within the body. Thisis of importance not only with regard to the interaction of the coatingof the medical device per se with its environment within the body, butis also necessary to maintain an even prolonged release of therapeuticagents.

Hardening by hydrogenation is a common process to increase the meltingprofile of fatty acids. Hydrogenation can be partial or result incomplete saturation of all double bonds. One particular way of obtainingthe appropriate properties of the fatty acids coating composition of thepresent invention, is by incomplete hydrogenation. Thus, in accordancewith a particular embodiment of the present invention, the melting pointof the fatty acid is raised to above body temperature by controlledincomplete trans-free hydrogenation. Incomplete hydrogenation is awell-described flexible process whereby the nature of the products isdetermined by the nature of the starting material, the extent ofhydrogenation and the selectivity. These parameters are controlled bythe process conditions and the nature of the catalyst used (Gunstone F.1999, Chapter 4: “Processing of Fatty Acids and Lipids”, in “Fatty Acidand Lipid Chemistry”, Aspen Publishers Inc., Gaithersburg, Md.). Theprocess of hydrogenation can be monitored by tracking the amount ofhydrogen consumed, by iodine value, the refractive index, by measuringthe solid fatty acid content by NMR, measuring the solid fat index bydilatometry, determination of the slip melting point and/or gaschromatography of the methyl esters. With the hydrogenation processesused industrially, isomerisation of the carbon-carbon double bonds inthe fatty acid residues occurs, beside the saturation of double bonds bythe addition of hydrogen. Thus, even if the starting material does notcontain any trans-isomers (as is the case of fatty acids from somebiological origins), hydrogenation by means of metal catalysts willinevitably result in cis/trans isomerisation. However, using the methodas described in WO 98/54275, hydrogenation can be carried out withselective adsorption of trans-isomers, ensuring an essentiallytrans-free cis-hydrogenated fatty acid composition.

Hence, it is a particular aspect of the present invention to prepare acoating material or a component of a coating material for a human orveterinary medical device, especially a device which is to be introducedinto or implanted in a human or animal body, especially such a device aswill come into contact with circulating blood supply and moreparticularly to a device which provides drug release, e.g. a deviceincorporating biologically active, therapeutic or similar agents in thecoating, by firstly providing a fat or oil with a melting point below37° C. and to trans-free hydrogenate such oil or fat to raise themelting point, e.g. to greater than 40° C. and less than 50° C. Ideally,the coating should not be molten at body temperature. The hydrogenationprocess is well characterised and is well suited to targeting themelting point range. In particular, natural materials such as fats oftenhave three states close to the melting point: a higher temperature statein which the material is molten, a lower temperature state in which thematerial is recognisable solid and an intermediate or “thermoplastic”state in which it exhibits some solid and plastic properties. It isparticularly preferred if the coating is in a thermoplastic state whenin contact with body tissue, i.e. at or near the blood temperature. Inaddition, drug and excipient loadings may affect the thermo mechanicalproperties of the coating, particularly when the drug is a lipophilicliquid. In accordance with a further aspect of the present inventiontrans-free incomplete hydrogenation of the starting material is soselected and controlled that the final drug/excipient coating materialmixture is in a thermoplastic state at body temperature, e.g. in therange 32 to 43° C., i.e. not in a liquid state in this range.

Further, it is a particular aspect of the present invention to controlthe thermo-mechanical properties of the coating materials so as todetermine, select or set a drug elution profile by trans-freehydrogenation of an oil or fat, especially a cis-hydrogenated fatty acidcomposition.

Additionally or alternatively the desired consistency of the fatty acidcoating composition can be influenced by the chain length of the fattyacids. The melting point of fatty acids increases with the number ofcarbon atoms (e.g. Butyric 7.9° C. (4c), Lauric 44.2° C. (12c), Stearic69.6° C. (18c), Behenic 79.7° C. (22c)). Moreover odd chain fatty acidsusually melt at a lower temperature than do the even chain acidscontaining one less carbon.

The desired consistency of the fatty acid coating composition can alsobe obtained by mixing of different components. For instance,triglycerides, which correspond to a glycerol attached to three fattyacids by separate ester bonds) can have different combinations ofdifferent fatty acids. By combining fatty acids of different chainlengths and number of double bonds, the desired melting point can beobtained.

According to the present invention, compounds comprisingcis-hydrogenated fats are used for the coating of implantable medicaldevices. The term coating as used herein can optionally refer to theapplication of a uniform layer over all or part of the medical device.Different methods of applying coatings are envisaged within the contextof the invention, including dip coating, inkjet printing, painting andspray coating. According to a particular embodiment the cis-hydrogenatedfats are mixed with a solvent, such as ethanol, where after the medicaldevice is dipped into the oil/ethanol solution. The solvent is thenevaporated under a heated airflow. Moreover, according to the presentinvention, different layers of cis-hydrogenated fats of the same ordifferent composition can be applied, optionally separated byintermediate layers. This can be of interest for the sequential releaseof drugs (see below).

A particular procedure for coating intraluminal prosthesis with a fat oran oil comprises the following steps:

1) Cleaning (for instance by sonicating in 3% Isopanasol and then indeionised (DI) water), degreasing (for instance by acetone) and dryingof the prosthesis

2) Dipping of the prosthesis in a sodium bicarbonate solution (forinstance 30 seconds) and air-dry

3) Making a solution or an emulsion of a biocompatible oil and a solventof for example pure ethanol

4) In this solution or emulsion a therapeutic agent can optionally bedissolved.

5) Applying to the prosthesis body of the therapeutic agent containingthe oil/solvent emulsion using dip coating or spray coating or any othercoating method. The prosthesis can be previously coated with zeolites orzeogrids, which have optionally been loaded with one or more therapeuticagents; alternatively these are introduced into the emulsion of step 3.

6) Air dry till the solvent is evaporated

7) Eventually repeat these previous steps multiple times

8) Use the prosthesis immediately or further air dry the prosthesis in asterile laminar flow.

9) After drying the coated prosthesis can be sterilised. Either withethylene oxide or gamma irradiation.

Additionally or alternatively, coating of a medical device can refer tothe filling up of particular structures in the structure of the medicaldevice, for instance the filling up of pits or grooves on the exterior(i.e. the side in contact with the body structure to be supported) ofthe medical device.

Other components can be added to the coating comprising thecis-hydrogenated fat of the invention, such as, but not limited toanti-oxidants (e.g. tocopherol) and solvents (which are optionallyremoved before use). In the coating of the present invention, thecontent of the cis-hydrogenated fats is not specifically limited, but ispreferably 20-100% by weight, more preferably 70-100%.

According to the present invention the loading capacity of thecis-hydrogenated fat coatings for the drugs will be dependent on thehydrophilicity characteristics of the drug. It has been shown thatlipophilic drugs have a higher solubility in the cis-hydrogenated fattyacids and a higher maximal drug loading capacity than hydrophilic drugsin coronary vascular wall (Bennett M R. In-stent stenosis: pathology andimplications for the development of drug eluting stents. Heart. 2003;89; 218-224). The cis-hydrogenated fat-based coatings are shown topotentially release about 20% of a therapeutic agent within 24 hours,allowing a fast loading of the injured tissue surrounding the stentstrut. Local tissue drug concentrations rise quickly, and reacheffective tissue drug concentrations within 24 hours to prevent thepathologic reactions after stent implantation.

The present application further demonstrates that the coating withcis-hydrogenated fats can provide a drug release curve characterised bya 20% of total drug amount released within 24 hours, 50% within oneweek, and 80% within four weeks. These release characteristics are wellcorrelated with the pathologic processes induced by stent implantation.In a porcine model, after stent implantation, acute pathologic reactions(thrombus formation, inflammation) happen within five days, and subacute reactions (smooth muscle cell proliferation) happen within fourweeks. Thus, the drug release rate using the cis-hydrogenated fat-basedstent coating is appropriate, from a therapeutic point of view. It isfurthermore demonstrated that for some drugs a prolonged drug releaserate over 6 weeks can be obtained.

The provision of several layers of coatings with cis-hydrogenated fatsof the same or different compositions allows the modulation of therelease of one or several drugs from the stent. In particular, thethermo mechanical properties of each layer may be controlled, selectedor determined by the degree of trans-free incomplete hydrogenation ofthe material of each layer so as to achieve a specific drug elutingprofile for each layer. Alternatively, the coating with cis-hydrogenatedfats of the present invention can be combined with other bio-degradablecoatings to ensure different release rates of one or more drugs from thecoating.

The amount of therapeutic agent to be included in the coating of thestent will be determined by the therapeutic effect envisaged and therelease curve of the therapeutic agent from the coating. Generally, forstents coated over their entire surface, the therapeutic agent will bepresent in the coating in an amount ranging from about 0.01 mg to about10 mg and more preferably from about 0.1 mg to about 4 mg of thetherapeutic agent per cm² of the gross surface area of the stent. “Grosssurface area” refers to the area calculated from the gross or overallextent of the structure, and not necessarily to the actual surface areaof the particular shape or individual parts of the structure. In otherterms, about 100 micrograms to about 300 micrograms of therapeutic agentper 0.002 cm of coating thickness may be contained on the stent surface.

The evaluation of stents with a coating that contains (drug-loaded)zeolites or zeogrids can be performed in an animal model, such as aporcine coronary model.

Stent implantation in the right coronary artery, left anteriordescending or left circumflex can be performed according to the methoddescribed by De Scheerder et al. in “Local angiopeptin delivery usingcoated stents reduces neointimal proliferation in overstretched porcinecoronary arteries.” J. Inves. Cardiol. 8:215-222; 1996, and in“Experimental study of thrombogenicity and foreign body reaction inducedby heparin-coated coronary stents.” Circulation 95:1549-1553; 1997. Theguiding catheter is used as a reference to obtain an over-sizing.

The evaluation can include both an acute study and a chronic study. Inthe acute study, control bare stents, CHFA-coated stents, stents coatedwith drug-loaded CHFA, stents coated with CHFA that contains molecularsieves and stents coated with CHFA that contains drug-loaded molecularsieves are randomly implanted in coronary arteries of pigs. Pigs aresacrificed after 5 days to evaluate acute inflammatory response andthrombus formation. In the chronic study, control bare stents,CHFA-coated stents, stents coated with drug-loaded CHFA, stents coatedwith CHFA that contains molecular sieves and stents coated with CHFAthat contains drug-loaded molecular sieves are randomly implanted incoronary arteries of pigs. Pigs are sacrificed after 4 weeks to evaluateperi-strut injury and in-stent neointimal hyperplasia.

Different parameters can be taken into consideration. Optionally,quantitative coronary angiography can be performed, before, immediatelyafter stenting and at sacrifice using the Polytron 1000®-system. ThePolytron has earlier been validated in vitro and in vivo with a metalbar as a calibration device. The diameter of the stented vessel segmentis measured. The degree of over-sizing is expressed as balloon/arterythickness ratio. Stent recoil is measured as:$\frac{{balloon} + {stent} - {stent}}{{balloon} + {stent}}$

To evaluate histopathology and morphometry, the pigs are sacrificed andthe stented coronary segments are carefully dissected together with an 1cm minimum vessel segment both proximal and distal to the stent afterpressure fixation using a 10% formalin solution at 80 mmHg. The segmentcan be fixated in a 2% formalin solution. The sections are embedded inplastic and stained with hematoxylin-eosin, elastica von Gieson, PTAHand Mason's trichrome stain for light microscopic examination.

Damage of the arterial wall can be graded as:

-   -   no disruption of the elastic membranes,    -   disruption of the internal but not the external elastic        membrane, or    -   disruption of both elastic membranes.        Neointimal proliferation within the stented vessel segments can        visually graded as:    -   presence of a thin fibromuscular layer covered by new        endothelium without noticeable    -   narrowing of the lumen.    -   neointimal proliferation leading to vessel lumen narrowing        estimated to be less than 50%, or    -   neointimal proliferation leading to vessel lumen narrowing        estimated to be greater than 50%.        In addition, the predominant histological events (organisation        of thrombus, histiolymphocytic reaction, fibromuscular reaction)        leading to the luminal obliterations can be carefully examined.        Morphometric analysis of the coronary segments harvested can be        performed using a computerised morphometry program (Leitz CBA        8000).        Measurements of maximal intimal thickening, the area within the        lumen (lumen area) and inside the internal elastic lamina        (intimal area) and external elastic lamina are performed on the        arterial sites, visually appreciated as being the most        proliferative.

BRIEF DESCRIPTION OF THE FIGURES

The following examples, not intended to limit the invention to specificembodiments described, may be understood in conjunction with theaccompanying Figures, incorporated herein by reference, in which:

FIG. 1: XRD pattern of precipitate (a), of intermediate product from thecalcination (b) and of final zeogrid (c) prepared using CTMABr (blacktrace) and DTMABr (grey trace) surfactants.

FIG. 2: SEM pictures of zeogrid precipitate, magnification 1,250× (a)and calcined product at magnifications of 1.250× (b) and 5,000× (c).

FIG. 3: β-Estradiol release from zeogrid against time (a) and againstsquare root of time (b).

FIG. 4: β-Estradiol release from zeogrid in a silicone coating. Threedrug doses are tested: 2.3 mg (a), 4.5 mg (b) and 9.1 mg (c)

FIG. 5: System for testing the attachment

FIG. 6: Graphic overview of the attachment strength of silicon coatingat Ti, RVS and Al depending on the pre-treatment of the surface of thesubstrate.

FIG. 7: Typical tension replacement curve of Ti, RVS and Al with asilicon coating.

FIG. 8: (A) Top plan view on tubular prosthesis that has been cut in itslongitudinal direction and pressed into a flat screen, the screenshowing the holes (reservoirs) in the outer surfaces of the prosthesis.(B) Illustration on a larger scale and in a cross sectional view of theholes in the strut. The holes are filled by a matrix comprising zeogridparticles; (1) substrate (for instance the struts of an expandablestent), (2) holes (reservoirs) in the substrate (in various shapesperforating or non-perforating as an illustration of differentembodiments), (3) a matrix comprising zeogrid particles filling theholes, (4) an optional coating on the surface of the substrate andsealing the holes

FIG. 9: Display of a substrate (for instance the struts of a expandablestent) (1), holes (reservoirs) in the substrate (in various shapesperforating or non perforating as an illustration of differentembodiments) (2), a matrix comprising grid particles filling the holes(3), an optional coating on the surface of the substrate and sealing theholes (4) and zeogrid (5) comprising drug (6).

FIG. 10: Linear regression analysis of (A) the correlation betweenarterial injury and neointimal hyperplasia for bare stents, coating Aand coating B; and (B) the correlation between arterial injury andneointimal hyperplasia for Ziscoat 5% and Ziscoat 10% coated stents

FIG. 11: Release curves of methylprednisolone (MPS) from the followingsamples: MPS directly embedded in a Ciscoat matrix; MPS embedded withina molecular sieve embedded in a Ciscoat matrix; MPS embedded bothdirectly in the matrix and in the molecular sieve particles comprisedtherein;

FIG. 12: Release curves of methylprednisolone (MP) from the followingsamples: MP directly embedded in a Ciscoat matrix; MP embedded within amolecular sieve (Drug-containing substrate or DCS) embedded in a Ciscoatmatrix; MP embedded both directly in the matrix and in the molecularsieve particles comprised therein;

EXAMPLES Example 1 Production of Zeogrids

An alternative approach to synthesize nanoscopically arranged molecularsieve material is reported.

A suspension of Silicalite-1 type zeosil nanoslabs was preparedfollowing a recipe from literature (C. E. A. Kirschhock et al, Angew.Chem. Int. Ed. 2001, 40, 2637; R. Ravishankar, et al, J. Phys. Chem. B1999, 103, 4960). This nanoslab suspension was diluted with ethanol.Saturated solution of cetyltrimethylammoniumbromide (CTMABr) in ethanolwas slowly added to the stirred suspension until a white precipitateformed. The precipitate was recovered by filtration, washed with ethanoland dried. The XRD pattern of the precipitate (FIG. 1 a, black trace)revealed the presence of a layered compound showing first and secondorder diffraction and having a repeat distance of 4.0 nm. Theprecipitate was heated under flowing oxygen gas to 150° C. and keptunder those conditions for 7 days. The sample was cooled to ambienttemperature. At this intermediate stage of the calcination, the compoundhad a brownish color. Part of the product was kept aside forcharacterization, the remaining part was heated under a flow of nitrogengas to 400° C. for 1 day and then cooled to 150° C. The sample was blackowing to carbonaceous residue left after pyrolysis of the organicmolecules. In the last step of the calcination procedure using flowingoxygen, the temperature was raised to 400° C., kept at this value for 2days to obtain the final white product, denoted as the zeogrid. The XRDpattern at the intermediate stage (FIG. 1 b, black trace) revealed thatthe repeat distance shrunk from the original 4.0 nm to 3.0 nm. The finalsample displayed also a repeat distance of ca. 3.0 mm (FIG. 1 c, blacktrace). In the final product, only the first reflection (100) of thesuperstructure was clearly observed (FIG. 1 c, black trace). Bragg typediffraction of crystalline material at wider angles was not observed.

SEM pictures revealed that the precipitate (FIG. 2 a) consisted ofspherical particles with diameters from 1 to 6 μm. After calcination(FIG. 2 b, c), the particles were reduced in size. Some particles showedfissures; others were disintegrated.

In another preparation, CTMABr was substituted withdodecyltrimethylammonium bromide (DTMABr). The XRD patterns ofprecipitate and final product again revealed the presence of a layeredcompound. In the precipitate, the repeat distance obtained with DTMABrwas only 3.2 nm compared to 4.0 nm with CTMABr (FIG. 1 a, grey trace).The XRD patterns of the intermediate and final product obtained withDTMABr were similar to the ones obtained with CTMABr with a repeatdistance of 3.0 μm (FIG. 1 b, c, grey traces). The absence of Braggreflections at higher angles clearly shows that before or duringcalcination no domains larger than about 15 nm with undisturbedSilicalite-1 structure have been formed.

The original nanoslab suspension was obtained by hydrolysing 37.32 gTEOS (Acros, 98%) in 32.13 g aqueous TPAOH solution (Alfa, 40 wt.- %)under continuous stirring. After the hydrolysis recognized by thehomogenization of the two liquids, 30.55 g de-ionized water was addedand stirring continued for 24 h.

To an amount of 20 mL of this suspension, a same volume of ethanol(technical grade) was added. Subsequently, 60 mL of a saturated solutionof cetyltrimethylammonium bromide (CTMABr, Acros, 99%+) in ethanol wasadded dropwise under stirring (5 mL/h). A white precipitate formedduring CTMABr addition.

In the experiment with DTMABr, a solution of dodecyltrimethylammoniumbromide (DTMABr, Acros, 99%) in ethanol (same concentration as theCTMABr experiment) was added. A white precipitate formed overnight.

The precipitates were recovered by filtration over 8 μm pore diameterpaper (Whatman 1440 090, grade 40), washed with ethanol on the filterand dried at 60° C. Calcination procedure. The precipitate wascompressed into flakes and the flakes crushed and sieved in order toobtain particles with diameters of 0.25-0.5 mm. An amount of 1 g ofsample was loaded as a packed bed in a quartz tube and subjected to thecalcination program. The heating rate was 0.5° C./min and the gas flow35 mL/min.

Example 2 Coating of Implantable Devices with a Zeogrid and a Matrix ofSilicone Elastomer

Preparation Method for Coated Ti-Plates

Materials

PDMS-silicone network was synthesised from the following precursors: asiliciumhydride polymer (RTV615B, General Electric Bayer), asiliciumvinyl polymer (RTV615A, General Electric Bayer) and a source ofextra hydrides (NM4214). Thin titanium plates were used. The dimensionsdepended on the experiment-type: 40 mm×20 mm×2 mm for mechanical testsand 15 mm×7 mm×150 μm for in vivo biocompatibility tests.

Alternatively silicone elastomer solutions can be made with DAP® 100%silicone rubber adhesive (from DAP, Inc., Maryland).

Alternatively the adjuvant polymers can be incorporated into thesilicone network. Such adjuvant polymerscan for instance be polyethyleneglycol (PEG) having a molecular weight preferably of about 2 KDa to 1MDa and most preferably about 2-500 KDa, copolymers of ethylene oxideand propylene oxide (EO/PO) such as Pluronic® polymers which exhibitsurfactant properties, as exemplified below, as well as any otherhydrophilic polymers, including, but not limited to, polysaccharidessuch a hyaluronic acid and chemically modified cellulose, polyamyloses,polydextroses, dextrans, heparins, heparans, chondroitin sulfate,dermatan sulfate, poly(N-isopropylacrylamide), polyurethanes,polyacrylates, polyethyleneimines, polyvinylpyrrolidone,polyvinylalcohol, polyvinylacetate, etc.

For instance the silicone can be dissolved with the adjuvant such aspolyethylene glycol of about 2-500 Kda for instance MW 3400 (PEG) inmethylene chloride. For instance 20% (w/w) of such PEG.

Surface Pre-Treatment

The plates were first acid pickled in a solution containing 40 ml HNO₃(65%) and 2 ml HF (38-40%) for 6 minutes in order to remove the titaniaoxide layer (Zhao et al., 2001), followed by an ultrasonic treatment indistillated water to remove any acid traces. The plates were thenchemically treated with a solution containing 8.8 M H₂O₂ and 0.1 M HClat 80° C. for 1 hour to obtain a cracked titania gel layer (Wang et al.,2002). Just before coating the plates were dried with an Argon flux.

Synthesis Coating Mixture

0.2 g zeogrid were suspended in 0.5 g MIBK (methyl isobutyl ketone). Thesuspension was homogenised for 10 minutes to obtain finally suspendedzeogrid particles. 0.2 g hydrides (NM) were added. This mixture wasstirred for 5 minutes in order to bind the zeogrid to the siliconeaccording to the following reaction:ZG-OH+Si—H→ZG-O—Si+H₂

Gas and heat formation confirms the reaction. In the last step 0.1 gextra hydrides (RTV615B) and 1 g vinyls (RTV615A) were added. Thismixture was stirred for 20 seconds.

To obtain a silicone mixture without zeogrid the same procedure wasfollowed, except that no zeogrid was added to the synthesis mixture.

Coating Procedure

A spincoater was used to create a thin homogeneous coating.

The pre-treated plates were wetted with a thick zeogrid-silicone mixturelayer (or just a silicone layer) to cover the whole surface. This layerwas spincoated on the plates at 400 to 1300 rpm. A thin homogeneouslayer was obtained. The thickness depended on the rotational speed. At1300 rpm the thickness was about 50 μm (Villani, 2002). For mechanicalexperiments the adopted rotational speed was 400 rpm. Forbiocompatibility experiments the adopted speed was 1000 rpm. To cure thesilicone network the plates were heated at a rate of 1° C. per minute to140° C. This temperature was maintained for approximately 12 hours.

Attachment of Silicone on Ti

Two different treatments of the surface of Ti plates have been tested.The first treatment comprises a treatment with HF and a second treatmentcomprises a treatment with HNO₃.

The distinction between “single” and “double” comes for from thedifferent test samples which are made for the joining (attachment)tests. At a “single” sample on one plate silicon layer is introduced andwith epoxy glue one attaches a second plate for the tearing test. At“double” samples two Ti-plates are directly joined by silicone. There nomore adhesive used for this “double” samples. A blanco Ti-plates gluedto each others with epoxy adhesive is used as reference. This way alsothe attachment strength of the adhesive to Ti is known.

Testing the Attachment

The system for testing the attachment is shown in FIG. 5.

Results

From the tension-replacement curve (FIG. 7) the maximal tear tension wascalculated, using the Von Mises criterium. This is considered avalidated value for the strength of attachment. The results aredemonstrated in Table 1 and FIG. 6. TABLE 1 Overview of the strength ofattachment of silicone at Ti, RVS and Al depending on the surfacetreatment of the substrate. Attachment strength Material Treatment (MPa)Ti HF-single >6.14 ± 2.62* Ti HNO₃-single 7.52 ± 2.59 Ti HF-double 11.81± 2.39  Ti HNO₃-double 7.83 ± 2.26 Al HNO₃-double 1.12 ± 0.47 RVSHF/HNO₃-double 6.67 ± 2.75 Ref Epoxy-glue 12.73 ± 0.74 

The results are demonstrated in FIG. 7 as a typical tension replacementcurve of Ti, RVS and Al with a silicone coating. The treatment of Tiwith HF ensures a better joining between the substrate and the siliconecoating. This is shown by both the results of only glued and the twiceglued samples. At the only glued samples it is each time the adhesivewhich breaks down and never the silicon-Ti interface. This means thatthe attachment strength amount to at least 6.2 MPa. In the group ofsubstrates with HNO3 treated surfaces there are samples on which thesilicone-Ti interface breaks down. This is an indirect indication thatHF-treatment realises a more stable interface. More direct indicationscome of the twice-glued samples, where always the silicon-Ti interfacebroke down. HF-treated samples had an attachment strength of 11.8 MPaand HNO3 treated samples only an attachment strength of 7.83 MPa. Boththe HF and the HNO3 treatments had more impact on the joining of Ti andsilicon than the other metal (Al and RVS). The attachment strength ofsilicon joined on Ti was significantly higher than Al and RVS.

Example 3 β-Estradiol Release from Zeogrid

Loading of the zeogrid sample with β-estradiol proceeds as follows. 50mg β-estradiol is dissolved in 100 ml methylenechloride. 500 mg ofzeogrid is suspended in the solution. Everything is stirred during 24hours in a closed container. After 24 hours, the container is opened andthe methylenechloride is evaporated at room temperature. The resultingpowder is further dried and kept during 24 hours under reduced pressureto remove the solvent.

Release of β-estradiol from zeogrids. Simulated body fluid (SBF) wasused as dissolution medium. SBF was prepared by first dissolving 1% SLS(Sodium lauryl sulphate) and 0.90% NaCl in distilled water. The solutionwas mixed with ethanol in a volume ratio solution:ethanol of 24:1.

The in-vitro release experiments were carried out at room temperature bydispersing 10 mg quantities of the loaded zeogrid into 20 ml quantitiesof SBF. In order to avoid limitations of the delivery rate by externaldiffusion constraints, continuous stirring is maintained. The releaseprofile was obtained by measuring drug concentration in the fluid afterdifferent times by means of HPLC.

FIG. 3 a shows the percentage of β-estradiol release from the zeogridsample against time. The release of β-estradiol from zeogrid iscompleted after 30 minutes. β-estradiol release against square root oftime is presented in FIG. 3 b. The linear relation between concentrationof β-estradiol in solution and square root of time reveals that the drugrelease if governed by diffusion through the pores of the zeogrid.

Slower release of the β-estradiol can be obtained by dispersing thedrug-loaded zeogrids in a coating, f.i. a silicone coating:

Metal plates are coated with silicone/zeogrid loaded with β-estradioland put in the release medium. Every day, the release medium is replacedand is analysed with HPLC to determine the concentration of β-estradiol.The test is performed in double. Three drug densities are tested:

Plate A (2.3 mg drug), Plate B (4.5 mg drug), plate C (9.1 mg drug).Drug-release curves are shown in FIG. 4 (a, b, c).

Example 4 Coating of a Stent with a Cis-Hydrogenated Fatty Acid (CHFA)Based Coating that Contains Zeogrids

The method to producing CHFA-based coating is described in WO 98/65275.Following steps are required to coat a medical device with aCHFA-coating that contains drug-loaded zeogrids:

-   -   a) Cleaning, degreasing and drying of the prosthesis    -   b) Dipping of the prosthesis in a deoxidative solution and air        drying it. Eventually, this step can be omitted.    -   c) Loading the zeogrids with the required therapeutic agent.    -   d) Mixing of drug-loaded zeogrids into the CHFA-based coating.        This is preferably performed after the last step of the        production of the CHFA, when the CHFA is still in the liquid        phase.    -   e) Making an emulsion or solution of the soya oil-based        cis-hydrogenated fatty acid based coating that contains        drug-loaded zeogrids and a solvent, preferably in a liquid state        of the cis-hydrogenated fatty acid based coating.    -   f) In this emulsion/solution, one or more therapeutic agents can        be dissolved when the CHFA-based coating did not yet contain a        therapeutic agent or one or more additional therapeutic agents        may be dissolved when the CHFA already contained one or more        therapeutic agents. The therapeutic substance needs only to be        dispersed throughout the solvent/CHFA emulsion or solution so        that it may be either in a true solution with the solvent/CHFA        emulsion or solution or dispersed in fine particles in the        solvent/CHFA emulsion or solution.    -   g) Stirring of the obtained solution until achievement of a        homogeneous mixture/solution    -   h) Applying to the prosthesis body of the therapeutic agent        containing solvent/CHFA emulsion or solution using dip coating        or spray coating or any other coating method.    -   i) Air-dry until the solvent is evaporated.    -   j) Optionally, the previous steps are repeated multiple times,        eventually using different therapeutic agents.    -   k) Further air-dry the prosthesis (in a sterile, laminar flow).        After drying, a topcoat can be applied by using dip coating,        spray coating or any other coating method.        After drying, the obtained coated prosthesis can be used as such        or further dried and sterilized. Light-protection is advisable        to maintain the biocompatible characteristics when stored.

Example 5 Pre-Clinical Evaluation of Coronary Stent Dipcoated with aCis-Hydrogenated Fatty Acid Based Coating (Ciscoat) and of theCis-Hydrogenated Fatty Acid Loaded with a Molecular Sieve (Zeogrids)

Materials and Methods

Porcine Coronary Model

Domestic crossbred pigs of both sexes weighing 20-25 kg were used. Theywere fed with a standard natural grain diet without lipid or cholesterolsupplementation throughout the study. All animals were treated and caredfor in accordance with Belgium National Institute of Health Guide forcare and use of laboratory animals.

The pigs were sedated with azaperone 0.1 ml/kg (Stresnil®, JanssenPharmaceutics, Beerse, Belgium) and anesthetized with intravenousketamine (Ketalar®, Parke Davis, Morris Plains, N.J., Warner Lambert,Belgium, 5 mg/kg) for induction and a mixture of ketamine at a rate of0.1 mg/kg/hr and 10 mg/ml Propofol (Diprivan® 1%, NV AstraZeneca SA,Belgium) at a rate of 2 mg/kg/hr for maintenance intravenously. Adequateanesthesia was determined by the loss of the limb withdrawal reflex. Thepigs were intubated in 6 F tracheal tubes and ventilation (Mark 7A®,Bird Cooperation®, Palm Springs, Calif.) was started using a mixture of20 vol. % of pure oxygen and 80 vol. % of room air. Continuouselectrocardiography and pressure were performed throughout theprocedure. An external carotid artery was surgically exposed and an 8Fr. intra-arterial sheath was introduced over a 0.035″ guide wire.Heparin 10000. IU and 900 mg lysin acetylsalicylas (Aspegic®),Sanofi-synthelabo S.A.N.V., Brussel, Belgium) were administeredintravenously as a bolus. The coronary artery was visualized using an 8Fr. Judkins L 3.0 catheter and Hexabrix was used as contrast agent. Thestents were mounted on a conventional coronary angioplasty ballooncatheter and then deployed in a selected arterial segment using aninflation pressure of 8 atm. for 30 seconds. Coronary angiography, afterintra-arterial administration of nitroglycerine (0.25 mg), was performedto confirm vessel patency after stent implantation. Finally, the carotidarteriotomy was repaired and the dermal layers were closed usingstandard technique.

The pigs were sacrificed by using an intravenous bolus of 20 mloversaturated potassium chloride. For these follow-up studies, theinstrumentation of the pigs was identical to those used during theimplantation procedure.

Stent Implantation

In the first study bare stents, coating A (5 min hydrogenation time) andcoating B (30 min hydrogenation time) stents (each group, n=2) wereimplanted in the coronary arteries of 2 pigs and followed for 5 days toevaluate inflammatory response and thrombus formation. Furthermore barestents (n=2), coating A (n=5) and coating B (n=4) stents were implantedrandomly in the coronary arteries of pigs. Pigs were sacrificed after 4weeks to evaluate peri-strut inflammation and neointimal hyperplasia.

In the second study Ciscoat C was used (15 min hydrogenation time) asCiscoat. Ciscoat mixed with 5% wt % Zeogrids (Ziscoat 5%, n=6), mixedwith 10% wt % Zeogrids (Ziscoat 10%, n=7) and Ciscoat C coated (Ciscoat,n=6) stents were implanted in the coronary arteries of 6 pigs. Pigs weresacrificed after 4 weeks to evaluate peri-strut inflammation andneointimal hyperplasia.

Stent implantation in the right coronary artery or/and left anteriordescending and the circumflex coronary artery was performed randomly.The guiding catheter was used as a reference to obtain an oversizingfrom 10 to 30%.

Measurements

Histopathology

At follow-up, the stented artery segment will be carefully dissectedtogether with an 1 cm minimum vessel segment both proximal and distal tothe stent after pressure fixation using a 10% formalin solution at 80mmHg. The segment will be fixated in a 5% formalin solution. Thesections will be embedded in plastic (Technovit). Sections from eacharterial segment will be stained with hematoxylin-eosin, elastica vonGieson, PTAH and Mason's trichrome stain. Light microscopic examinationwas performed by an experienced pathologist who was blinded to the typeof stent used. Injury of the arterial wall due to stent deployment (andeventually inflammation induced by the polymer) was evaluated for eachstent filament and graded as described.

Grade 0=internal elastic membrane intact;

Grade 1=internal elastic membrane lacerated, media compressed but notlacerated;

Grade 2=media visibly lacerated, external elastic membrane compressedbut intact;

Grade 3=external elastic membrane lacerated or stent filament residingin the adventitia. Inflammatory reaction at each stent filament wascarefully examined, searching for inflammatory cells, and scored asfollowed:

1=sparsely located histolymphocytes surrounding the stent filament;

2=more densely located histolymphocytes covering the stent filament, butno lymphogranuloma and/or giant cells formation found;

3=diffusely located histolymphocytes, lymphogranuloma and/or giantcells, also invading the media.

Mean score=sum of score for each filament/number of filaments present.

Morphometry

Morphometric analysis of the coronary segments harvested was performedusing a computerized morphometry program (Leitz CBA 8000). Measurementsof lumen area, lumen area inside the internal elastic lamina, and lumeninside the external elastic lamina were performed. Furthermore, areastenosis and neointimal hyperplasia area were calculated.

The ratio of balloon area/internal elastic lamina area (Bal-a/IEL-a) wasapplied to provide the normalized value of oversizing related to theextent of mechanic arterial injury during stent implantation.

Statistics

Data are presented as mean values ±SD, n represents the number ofstents. The histological and morphometric values of each stent arecalculated, and the linear regression of arterial injury with neointimalhyperplasia for bare stents and for the mean values of coating A and B,for Ciscoat coated and for the mean values of Ziscoat 5% and Ziscoat 10%are performed. As the number of stents in the first study is limited, nostatistic comparison is performed among the groups. In the second studyone-way analysis of variance (ANOVA) followed by Dunnett's post-hoc wasused for comparison. A p value<0.05 is considered as statisticallysignificant.

A. First Study—Aims

-   -   1. Evaluation of early inflammatory response and thrombus        formation of Ciscoat coated stents (coating A (5 min        hydrogenation time) and coating B (30 min hydrogenation time) in        a porcine coronary artery at 5 days    -   2. Evaluation of in-stent neointimal hyperplasia of        Ciscoat-coated stents at 4 weeks in a porcine coronary model    -   3. Comparison of non-coated stents with coating A and coating B        stents        Results

All stents were implanted successfully. No dissection noted by coronaryangiography and other complications were observed. All pigs weresacrificed at the study end points.

Histopathology

In the first study, stent struts mild to moderate compressed internalelastic lamina and media were observed at 5 days. Medial layer laceratedwas noted at one section of coating A stent. Arterial injury was low andcomparable among the three groups (bare: 0.28±0.14, coating A:0.30±0.16, coating B: 0.26±0.14). Stent struts were covered by a thinthrombotic meshwork. The thrombus formation of coating A and B stentswas slightly higher than the bare stents (bare: 1.00±0.00, coating A:1.06±0.07, coating B: 1.12±0.07). Inflammatory cells were adhesive tothe injury site and infiltrated into the thrombotic meshwork. Peri-strutinflammation (bare: 1.00±0.00, coating A: 1.02±0.04, coating B:1.00±0.00) was comparable among the groups.

At 4 weeks follow-up (Table 2), the neointima of the bare, coating A andB stent groups consisted of smooth muscle cells within an extracellularmatrix. Increased arterial injury was observed in coating A and B groups(bare: 0.27±0.14, coating A: 0.41±0.23, coating B: 0.55±0.48). Laceratedmedial layer was found at one stent section of both coating A and Bgroups. Especially in one coating B stent (CISCOAT-5, LAD), laceratedexternal elastic lamina was observed. Inflammatory cells were presentaround the stent struts and neointima. The peri-strut inflammatoryresponse of the coating A stents (1.00±0.00) was unique and low.Increased peri-strut inflammatory response was found in the coating Bstent (CISCOAT-5, LAD). A few stent struts showed increased peri-strutinflammation scored as 3, which resulted in an increased inflammatoryscore of coating B stent group (bare: 1.08±0.29, coating A: 1.00±0.00,coating B: 1.24±0.44) and arterial injury.

Morphometry

In the first study (Table 2), the lumen area of coating A (5.58±2.12mm²) and coating B (5.11±1.88 mm²) stent groups was slightly lower thanthe bare stent group (5.95±1.69 mm²) at 4 weeks. Neointimal hyperplasia(bare: 1.46±0.28, coating A: 1.57±0.62, coating B: 1.64±1.16) and areastenosis of coating A and coating B were comparable to the bare stentgroup, although the oversizing (Balloon-a/IEL-a) of the coating A andcoating B stents was higher than the bare stents.

B. Second Study—Aims

-   -   1. Evaluation of the biocompatibility of Ciscoat C (15 min        hydrogenation time) loaded with 5% and 10% Zeogrids (Ziscoat)        coated stents in a porcine coronary model    -   2. Comparison of Ciscoat C loaded with 5% and 10% Zeogrids        (Ziscoat) coated stents with Ciscoat C coated stents        Results

In the second study (Table 3), the arterial injury of stent implantationwas low (Ciscoat 0.31±0.15, Ziscoat 5%: 0.41±0.26, Ziscoat 10%:0.31±0.21). Lacerated internal elastic lamina was observed in allsections. Some stent struts showed lacerated medial layer. In oneZiscoat 5% coated stent (Ziscoat-7, LCX), lacerated external lamina wasfound in a few stent struts. Meanwhile increased peri-strut inflammationwas observed in all proximal, middle and distal sections of this stents.Limited and unique peri-strut inflammation however was noted in allother stents (Ciscoat: 1.00±0.00, Ziscoat 5%: 1.12±0.27, Ziscoat 10%:1.00±0.00).

Morphometry

In the second study (Table 3), the lumen area of Ziscoat 10% coatedstents was larger than the Ciscoat and Ziscoat 5% coated stents(Ciscoat: 4.74±1.60, Ziscoat 5%: 4.32±1.65, Ziscoat 10%: 5.13±1.59).Furthermore the neointimal hyperplasia of Ziscoat 10% coated stents wasslightly lower then the other two groups. The neointimal hyperplasia ofZiscoat 5% coated stent (Ziscoat-7, LCX) was the highest (2.07 mm²),which was responsible to the increased neointimal hyperplasia of Ziscoat5% coated group (Ciscoat: 1.27±0.60, Ziscoat 5%: 1.42±0.63, Ziscoat 10%:1.09±0.42). Compared to the Ciscoat coated group, no differences oflumen area, neointimal hyperplasia, area stenosis were observed amongthe groups (P>0.05).

By linear regression of arterial injury with neointimal hyperplasia, themean values of neointimal hyperplasia for both coating A and coating Bare on the linear approximation of the bare stents (FIG. 10, A).Furthermore the mean values of neointimal hyperplasia for Ziscoat 5% andZiscoat 10% coated stents are on the linear approximation of the Ciscoatcoated stents (FIG. 10, B).

Conclusions

At 5 days, the coating A and B stents induced a similarhistopathological response and thrombus formation compared to the barestents.

At 4 weeks follow-up, one coating B and one Ziscoat 5% coated stentinduced severe peri-strut inflammation, resulting in an increasedarterial injury and neointimal hyperplasia, probably due tocontamination of the stent.

At 4 weeks, the peri-strut inflammation, neointimal hyperplasia and areastenosis of coating A and B stents were comparable to the bare stents.The Ziscoat 5% and Ziscoat 10% coated stents were comparable to theCiscoat coated stents.

Interestingly, it was found that the area stenosis was significantlylower for the Ziscoat 10% compared to the stents coated with Ciscoatalone. Thus, the zeogrids appear to have an anti-restenotic effect.

Using linear regression analysis comparing arterial injury withneointimal hyperplasia, the mean values of neointimal hyperplasia forboth A and B are on the linear approximation of the bare stents. Themean values of neointimal hyperplasia for Ziscoat 5% and Ziscoat 10%coated stents are on the linear approximation of the Ciscoat coatedstents.

Both 5 days and 4 weeks data showed that the function of coating A and Bstents was similar to the bare stents. Both coating A and B did notinduce increased inflammation and proliferative tissue response.

Adding 5% and 10% Zeogrids to Ciscoat coating did not influence thefunction of the coating material and show a good biocompatibility to thecoronary arterial wall.

It can be concluded from these studies that both Ciscoat and Ziscoat arebiocompatible coatings. TABLE 2 Histomorphometric analysis of Ciscoatstented vessel segments 4 weeks follow-up in porcine coronary arteries nLA (mm²) NIH(mm²) AS(%) Bal-a/IEL-a Inflammation Injury Bare 2 5.95 ±1.69 1.46 ± 0.28 21 ± 7  1.14 ± 0.09 1.08 ± 0.29 0.27 ± 0.14 Coating A 55.58 ± 2.12 1.57 ± 0.62 24 ± 12 1.24 ± 0.16 1.00 ± 0.00 0.41 ± 0.23Coating B 4 5.11 ± 1.88 1.64 ± 1.16 26 ± 21 1.25 ± 0.19 1.24 ± 0.44 0.55± 0.48LA = lumen area; NIH = neointimal hyperplasia,; AS = area stenosis; IEL= internal elastic lamina; Bal-a/IEL-a = balloon-area/IEL-area.

TABLE 3 Histomorphometric analysis of Ziscoat stented vessel segments 4weeks follow-up in porcine coronary arteries n LA (mm²) NIH(mm²) AS(%)Bal-a/IEL-a Inflammation Injury CISCOAT 6 4.74 ± 1.60 1.27 ± 0.60 23 ±13 1.43 ± 0.22 1.00 ± 0.00 0.31 ± 0.15 ZISCOAT 5% 6 4.32 ± 1.65 1.42 ±0.63 27 ± 16 1.47 ± 0.17 1.12 ± 0.27 0.41 ± 0.36 ZISCOAT 10% 7 5.13 ±1.59 1.09 ± 0.42 18 ± 8  1.35 ± 0.23 1.00 ± 0.00 0.31 ± 0.21One-way analysis of variance (ANOVA) followed by Dunnett's post-hoc wasused for comparison. The p values of all items were >0.05.LA = lumen area; NIH = neointimal hyperplasia,; AS = area stenosis; IEL= internal elastic lamina; Bal-a/IEL-a = balloon-area/IEL-area.

Example 6 In Vitro Release of Methylprednisolone (MP) andMethylprednisolone Sodium Succinate (MPS) from a Cis-Hydrogenated FattyAcid Based Coating (Ciscoat) and from a Molecular Sieve (Zeogrid)Optionally Comprised in a Cis-Hydrogenated Fatty Acid Based Coating

Methylprednisolone (MP) and Methylprednisolone succinate (MPS) (J PharmSci. 1987 July; 76(7):528-34. Toutain P L, et al.) are corticosteroids.Methylprednisolone is a hormone naturally produced by the adrenal glandswhich have many important functions, including control of inflammatoryresponses. Methylprednisolone sodium succinate is a syntheticcorticosteroid of the natural variant. It has the same metabolic andanti-inflammatory actions as the parent compound, methylprednisolone;but is a water-soluble ester salt.

Materials and Methods

The Experimental Groups:

1. (Ciscoat loaded with MP)

2. Ciscoat+(zeogrids loaded with MP=drug-containing substrate or DCS))

3. (Ciscoat loaded with MP)+(zeogrids loaded with MP)

4. (zeogrids (loaded with MP) without Ciscoat

5. (Ciscoat loaded with MPS)

6. Ciscoat+(zeogrids loaded with MPS)

7. (Ciscoat loaded with MPS)+(zeogrids loaded with MPS)

8. (zeogrids loaded with MPS) without Ciscoat

9. Ciscoat+(zeogrids loaded with MP)+(zeogrids loaded with MPS)

Preparation of the Drug Loaded Coatings

Zeogrid were loaded as follows: MP or MPS was solved in a solvent(dimethylether). The Zeogrids were impregnated with the solventcomprising the MP or the MPS. Consequently the solvent was evaporated.By this method the zeogrids were loaded with MP or MPS for 20% of theweight (1 mg loaded zeogrid contains about 200 μg of MP or MPS).

The cis-hydrogenated omega-3 fatty acid based coating (Ciscoat) wasprepared from soy oil according to the hydrogenation process describedin WO 98/54275 designed to significantly eliminate the formationtrans-unsaturated fatty acid compounds.

The metal carrier for the coating was a stainless steel plate with atotal surface of 1 cm² (front surface, back surface and surface of theedge). The samples 4 and 8 contain only zeogrid loaded with respectivelyMP and MPS, but no Ciscoat and metal carrier.

Every sample comprised about 200 μg MS or MPS. The loaded dose wascontrolled as follows: the metal carriers were dipped in melted Ciscoatat a temperature of 80° C., and weighed. A sample can carry 4.9 mgCiscoat. Thus 4.9 mg Ciscoat had to be arranged to comprise about 200 μgof MS or MPS.

Ciscoat was divided over small vials of precisely know weight (1.4 mlCiscoat/vial). The filled vials were weighed again to determine the massof Ciscoat. The masses are displayed hereunder in Table 4. TABLE 4 Vialnr. Mass empty Mass filled Mass fat 1 2.83963 4.05376 1.21413 2 2.842753.91444 1.07169 3 2.86723 3.94664 1.07941 4 5 2.84678 4.07397 1.22719 62.83381 3.89863 1.06482 7 2.88289 4.03484 1.15195 8 9 2.82885 3.886341.05749Weights in g

Knowing that 4.9 mg ciscoat had to comprise about 200 μg MP or MPS acorrect amount of zeogrid (ZS) loaded with MP or MPS had to be added tothe ciscoat (see hereunder in Table 5). TABLE 5 mass MP mass MP mass MPmass MP mass MPS mass MPS mass MPS mass MPS Vial nr. theor. real ZGtheor. ZG real theor. real theor ZG real ZG 1 49.556 49.58 — — — — — — 2— — 218.712 218.8 — — — — 3 22.028 21.97 110.145 110.15 — — — — 4 — — 11.01 — — — — — — 1.05 — — — — — — 1.03 — — — — 5 — — — — 50.089 50.16 —— 6 — — — — — — 217.31 217.22 7 — — — — 23.509 23.55 117.546 117.77 8 —— — — — — 1 1.02 — — — — — — 1.08 — — — — — — 1.03 9 — — 107.907 107.74— — 107.907 107.86Weights in mg

Since a homogenous solution was not obtained at the preparation of vial6 a new vial was prepared with half the dose of MPS (Vial 6B is), seetable 6 hereunder: TABLE 6 mass MP mass MP mass MP mass MP mass MPS massMPS mass MPS mass MPS Vial nr. theor. real ZG theor. ZG real theor. realtheor ZG real ZG 6 bis 118.405 118.51Weights in mg

The test samples were dipped in the melted Ciscoat at 80° C. comprisingMP or MPS (in triplicate per condition). After solidification of theCiscoat the samples were put in 10 ml volume test vials. For the samplesno. 4 and 8 an amount of MP or MPS loaded zeogrids adjusted to obtainthe same drug load were added to the test tube (in triplicate percondition). Except the sample no. 6, which comprised a drug load ofabout 100 μg, all other samples comprised about 200 μg of MP or MPS.

Results

The drug release was measured by HPLC. The release curves are cumulative(decreases in the curves are due to the fact that for every measure anew calibration curve was used) The ordinate of the original curves wasexpressed in mg/ml. The used volume is 10 ml. The graph (FIGS. 11 and12) display the total amount of drug released. Multiplication of thevalues by 10 provides the total amount of medicament that was released.

1-21. (canceled)
 22. A composition for coating an implantable medicaldevice, said composition comprising: a) a coating matrix, and b)particles of one or more molecular sieves, wherein said particles ofsaid one or more molecular sieves comprise, within their pores, one ormore bioactive agents.
 23. The composition of claim 22, for controlledrelease of a bioactive agent, wherein the size of said pores of said oneor more molecular sieve particles is selected to ensure controlledrelease rate of said bioactive agent.
 24. The composition of claim 22,wherein said coating matrix comprises one or more bioactive agents. 25.The composition of claim 24, wherein said one or more bioactive agentscomprised in said coating matrix is the same as one or more of saidbioactive agents comprised in said molecular sieve material.
 26. Thecomposition of claim 22, wherein said implantable medical device is astent.
 27. The composition of claim 22, wherein said molecular sieve isa silicate molecular sieve.
 28. The composition of claim 22, whereinsaid molecular sieve is a zeogrid.
 29. The composition of claim 22,wherein said coating matrix consists essentially of cis-hydrogenatedfatty acids.
 30. An implantable medical device coated with thecomposition of claim
 22. 31. The implantable medical device of claim 30,characterized in that said particles of said one or more molecularsieves are embedded within said matrix.
 32. The implantable medicaldevice of claim 30, characterized in that said particles of said one ormore molecular sieves are glued to the surface of said implantabledevice and are covered by said matrix.
 33. The implantable medicaldevice of claim 30, which comprises structural cavities on its innerand/or outer surface.
 34. The implantable medical device of claim 33,wherein said structural cavities are filled with said matrix.
 35. Theimplantable medical device of claim 33, wherein the surface of saidimplantable medical device is not coated with said coating composition,with the exception of said structural cavities.
 36. The implantablemedical device of claim 35, wherein the surface of said implantablemedical device is coated with a second matrix which is different fromthe matrix comprised in said structural cavities.
 37. A method forpreparing a coating composition for an implantable device, said methodcomprising a) providing i) a coating matrix, and ii) particles of one ormore molecular sieves, wherein said particles of said one or moremolecular sieves comprise, within their pores, one or more bioactiveagents b) mixing said coating matrix and said molecular sieve materialto obtain said coating composition
 38. The method of claim 37, whereinsaid coating matrix comprises a bioactive agent.
 39. A method fordelivering suitable amounts of one or more bioactive agents into a bodyportion during or following a medical procedure, said method comprising,introducing into said body portion an implantable medical deviceaccording to claim
 30. 40. The method according to claim 39, which is amethod of treatment of a patient at risk of prosthesis-inducedrestenosis.